1. Field of the Invention
The present invention relates to a trespass detection system that detects whether there is trespassing by a suspicious person or the like in a broad range of area such as a plant, substation or airport, and the position of the trespassing.
2. Description of the Related Art
Traditionally, as a trespass detection system for detecting whether there is trespassing by a suspicious person or the like and the position of the trespassing, plural surveillance camera are installed to detect whether there is trespassing (see, for example, JP-A-9-172630).
However, in the case where such surveillance cameras are used, the detection range and the timing of detection must be set by the position of the surveillance cameras, the position of images, or switching of the surveillance cameras. The accuracy of setting the detection range is poor and the way of setting is complicated. Moreover, as the surveillance range becomes broader, the number of surveillance cameras to be installed must be increased, which raises the cost. Therefore, the system is not suitable for detecting whether there is trespassing in a broad range of area such as a plant, substation or airport.
Thus, in order to enable detection of whether there is trespassing in a broad range of surveillance area such as a plant, substation or airport and the position of the trespassing, the present applicants have provided a trespass detection system in which a leakage transmission line on the transmitting side and a leakage transmission line on the receiving side are arranged parallel to each other at a predetermined spacing from each other so that a leakage electronic wave can be sent and received between the two sides. It is determined that there is trespassing when the electronic wave received on the leakage transmission line on the receiving side is changed, and the position of the trespassing can be specified (see, for example, JP-A-2004-309423).
In the trespass detection system described in JP-A-2004-309423, a threshold value must be set in advance for determination in trespass detection. For this setting of this threshold value, tests are repeated and the signal intensity and the quantity of change are measured when the system is installed, and a proper value is decided on the basis of the results of the measurement.
However, in the case where tests are repeated when the trespass detection system installed, and a threshold value is decided on the basis of the result of the measurement, as in the traditional technique, the measuring work is highly labor- and time-consuming.
Also, the electric wave environment may be changed by the influence of disturbance such as changes in weather conditions and the existence of a strong-field object. Therefore, the threshold that has once been set may not be proper for detecting trespassing. Thus, traditionally, it is necessary to conduct a work of manually updating to a proper threshold value each time in accordance with a change due to disturbance, and also in this respect, the work of changing the threshold value requires extra labor and time.